Direct write manufacturing (DWM) involves creating a pattern of active, passive and other functional components or elements directly onto a solid substrate, either by adding or removing material from the substrate, without utilizing a mask, pre-existing form, or tooling. DWM technologies were developed to answer the need of the microelectronics industry to have a means for rapidly prototyping circuit elements on various substrates. These elements are typically at the mesoscopic scale, i.e., within a size range between conventional microelectronics (sub-micron range) and traditional surface mount components (10+mm range). Although DWM may also be accomplished in the sub-micron range using electron beams or focused ion beams, these techniques are not appropriate for large scale rapid prototyping due to their small scale and, hence, low deposition rates.
One advantage of DWM technologies is the fact that it obviates the need to use a mask which is usually extremely expensive. Another advantage of such maskless processes is that they allow for electronic circuits or devices to be prototyped without iterations in the design and fabrication of photo-lithographic masks and allow for the rapid functional evaluation of circuits or devices. Still another advantage is their ability to help reduce the size of printed circuit boards and other devices through functional integration of minute active, passive and other functional elements. With DWM, it would be possible to incorporate electronic elements onto an odd-shaped substrate. Examples of interesting applications include conformal printing of communication circuits directly onto a soldier's helmet or eyeglass frame.
The direct write process can be controlled with CAD/CAM programs, thereby permitting electronic circuits to be fabricated by machinery operated by unskilled personnel or allowing designers to move quickly from a design to a working prototype. Meso-scaled DWM technologies are particularly useful in microelectronic fabrication of various circuit components. These components include (a) passive components such as insulator, resistor, capacitor, inductor, dielectric, and conductor; (b) active components such as diode, transistor, light-emitting element, electronic ink, photo-conductor, thermo-electric, superconductor, battery electrode, solar cell electrode, antenna, second harmonic generator, non-linear optic element, etc.; and (c) other functional elements such as ohmic contacts and interconnects for circuit, sensor elements, and actuator or effector elements. DWM is also useful for photolithographic mask repair, device restructuring and customization, and design and fault correction.
Prior art material-additive DWM technologies include ink jet printing, Micropen®, laser chemical vapor deposition (LCVD), focused CVD, laser engineered net shaping (LENS), laser-induced forward transfer (LIFT), and matrix-assisted pulse-laser evaporation (MAPLE). Currently known material-subtractive DWM technologies for removing material from a substrate include laser machining, laser trimming, and laser drilling.
In the “LIFT” process, a pulsed laser beam is directed through a laser-transparent target substrate to strike a film of material coated on the opposite side of the target substrate. The laser vaporizes the film material as the material absorbs the laser radiation. Due to the transfer of momentum, the material is removed from the target substrate and is redeposited on a receiving substrate that is placed in the vicinity of the target substrate. The “LIFT” process is typically used to transfer opaque thin films (typically metals), from a pre-coated laser transparent support (typically glass, SiO2, Al2O3, etc.), to the receiving substrate. Due to the film material being vaporized by the action of the laser, LIFT is inherently a homogeneous, pyrolytic technique and typically cannot be used to deposit complex crystalline or multi-component materials. Furthermore, because the material to be transferred is vaporized, it becomes more reactive and can more easily become degraded, oxidized or contaminated. The method is not well suited for the transfer of organic materials, since many organic materials are fragile and thermally labile and can be irreversibly damaged during deposition. Other shortcomings of the LIFT technique include poor uniformity, morphology, adhesion, and resolution. Further, because of the high temperatures involved in the process, there is a danger of ablation or sputtering of the support, which can cause the incorporation of impurities in the material being deposited on the receiving substrate.
Similarly, the MAPLE technique (U.S. Pat. No. 6,177,151, Jan. 23, 2001 to Chrisey, et al.) also involves depositing a transfer material onto a receiving substrate. The front surface of a target substrate has a coating that comprises a mixture of the transfer material to be deposited and a matrix material. The matrix material has the property that, when exposed to pulsed laser energy, it is more volatile than the transfer material. A pulsed laser energy is directed through the back surface of the target substrate and through a laser-transparent support to strike the coating at a defined location with sufficient energy to volatilize the matrix material at the location, causing the coating to desorb from the location and be lifted from the surface of the support. The receiving substrate is positioned in a spaced relation to the target substrate so that the transfer material in the desorbed coating can be deposited at a defined location on the receiving substrate. This technique requires a separate step for the preparation of a coating on a substrate. For some intended transfer materials, it may be difficult to find a suitable matrix material that is physically and chemically compatible with the transfer material so that the “lifting” procedure can be properly carried out. Since a pulsed laser is also used in the MAPLE technique, this technique suffers from similar drawbacks that are commonly associated with the LIFT process. Heavy and expensive equipment is required in these processes.
In U.S. Pat. No. 4,665,492, issued May 12, 1987, Masters teaches a freeform fabrication technique by spraying liquid resin droplets, a process commonly referred to as Ballistic Particle Modeling (BPM) for the purpose of rapid fabrication of a 3-D concept model (but not micro-electronic device). The BPM process includes heating a supply of thermoplastic resin to above its melting point and pumping the liquid resin to a nozzle, which ejects small liquid droplets from different directions to deposit on a substrate. Sanders Prototype, Inc. (Merrimack, N.H.) provides inkjet print-head technology for making plastic or wax models. Multiple-inkjet based rapid prototyping systems for making wax or plastic models are available from 3D Systems, Inc. (Valencia, Calif.). Model making from curable resins using an inkjet print-head is disclosed by Yamane, et al. (U.S. Pat. No. 5,059,266, October 1991 and U.S. Pat. No. 5,140,937, August 1992) and by Helinski (U.S. Pat. No. 5,136,515, August 1992). Inkjet printing involves ejecting fine polymer or wax droplets from a print-head nozzle that is either thermally activated or piezo-electrically activated.
Due to the limited allowable liquid viscosity range (typically up to 20 centi-poise, cps, only) of a printhead, 3-D inkjet printing has been limited to wax and other low-molecular weight polymers. Similarly, the print-head in a typical 2-D color image printing (onto a sheet of paper) is only capable of dispensing low-viscosity liquid such as a conventional ink which typically contains more than 99% by volume of water and less than 1% dye. These conventional print-heads for 2-D color printing or 3-D object printing are not directly amenable to the deposition of passive or active electronic components or elements onto a silicon or plastic substrate. These useful components include resistor, capacitor, dielectric, inductor, antenna, battery electrode, solar cell electrode, conductor or interconnect, and various sensor or actuator elements, etc. These components typically have too high a melting point to be workable, in a melt state, with an inkjet print-head which is constrained by a maximum operating temperature of approximately 200° C. Therefore, these components must be prepared in a precursor fluid form, which could be a metal-organic liquid (convertible to the desired component by heat and/or radiation), a solution (containing a solute component dissolved in a liquid), a suspension (solid particles dispersed but not dissolved in a liquid), or a sol-gel (colloidal fluid). These precursor fluids, when with a low solid content (or with a low proportion of the precursor material being actually converted into the final component), may be directly injectable by a conventional inkjet print-head, but resulting in extremely thin film deposited on a solid substrate. With such a low solid content fluid, it would require multiple passes (repeated dispensing and deposition onto the same area) to build a device component of a useful thickness. On the other hand, a precursor fluid containing a higher solid or desired component content normally has too high a fluid viscosity (easily greater than 20 cps) to be directly injectable by a conventional inkjet print-head.
In addition to the above-cited problem of being incapable of dispensing higher-viscosity or higher solid content fluid, the conventional inkjet printing devices suffer from the following shortcomings: (1) limited range of materials that can be inkjet printed and, hence, limited scope of application in direct writing of microelectronic components; and (2) difficulty or incapability in adjusting the fluid dispensing rate on demand or in real time during the component fabrication procedure.
Therefore, an object of the present invention is to provide an inkjet printing-based direct write process and apparatus for depositing active or passive components, in either a thin-film or a thick film form, onto a solid substrate for manufacturing a microelectronic device.
Another object of the present invention is to provide a computer-controlled process and apparatus for producing a multi-element device on a point-by-point basis.
Still another object of this invention is to provide a direct write technique that places minimal constraint on the range of materials that can be used in the fabrication of a device.
It is a further object of this invention to provide a computer-controlled device-fabricating process that does not require heavy and expensive equipment.
It is another object of this invention to provide a process and apparatus for building a CAD-defined device in which the material-dispensing rate can be readily varied on demand or in real time.